1. CELLS: The Building Blocks of Life

2. History of the Cell
Robert Hooke is a scientist from England.
He experimented with clocks, telescopes and microscopes.
He became famous for the observation of thin slices of bark through the microscope in 1667.
It was this observation that led him to….THE DISCOVERY OF THE CELL !

3. How did he discover the Cell?
He sharpened his knife as keen as a razor blade.
He cut off a very thin piece of cork with his knife.
He placed the thin piece of cork on a black object plate.
Through the microscope, he observed that the cork cells were perforated and porous, much like a honeycomb.

4. CORK CELLS

5. Microscopes Light microscope can magnify objects up to 1000 x
Thus, many organelles cannot be seen clearly
Electron microscope
can magnify objects up
to > x
Thus, many organelles can be seen more clearly

6. Micrographs What is it? A camera can be fitted to a microscope to
take pictures. This picture is called the
micrograph.

7. Micrographs Photomicrograph Taken using a light microscope
Pictures are in colour
Electronmicrograph
Taken using an electron microscope
Pictures are in black- and-white but images can be artificially colourised.

8. What does a cell consist of?

9. What does a cell consist of?
cell wall
cytoplasm
nucleus

10. What does a cell consist of ?
Protoplasm
Nucleus + Cell surface membrane + Cytoplasm
Organelles
- Specialised structures within the cell

11. Parts of a Cell The protoplasm of a cell is made up of three parts:
Cytoplasm
Protoplasm between the cell surface membrane and nucleus
Where most cell activities occur
Contains enzymes and specialised structures (organelles)
Cell surface membrane
Surrounds the cytoplasm
Partially permeable
Hence controls substances entering or leaving the cell
nucleoplasm nucleolus chromatin
nuclear envelope
Nucleus
Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin
Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

12. Cell surface membrane (plasma membrane)
Animal cell
Plant cell

13. Cell surface membrane (plasma membrane)
Photomicrograph
Cell surface membrane
Cheek cell
Onion epithelial cell

14. Cell wall
Non-living cell wall made of cellulose that encloses the entire plant cell, surrounding the cell membrane.
The cell wall is fully permeable and is absent in animal cells.
Function:
It protects the cell from injury and gives the plant cell a fixed shape.

15. What does a cell consist of?
Cell wall
Only exist in plant cells
Absent in animal cells

16. What does a cell consist of?
Photomicrograph
Cell wall

17. Parts of a Cell The protoplasm of a cell is made up of three parts:
Cytoplasm
Protoplasm between the cell surface membrane and nucleus
Where most cell activities occur
Contains enzymes and specialised structures (organelles)
Cell surface membrane
Surrounds the cytoplasm
Partially permeable
Hence controls substances entering or leaving the cell
nucleoplasm nucleolus chromatin
nuclear envelope
Nucleus
Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin
Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

18. Cytoplasm
Cytoplasm

19. Cytoplasm
Cytoplasm
Drawing of Onion epithelial cell
Cheek cell

20. Parts of a Cell The protoplasm of a cell is made up of three parts:
Cytoplasm
Protoplasm between the cell surface membrane and nucleus
Where most cell activities occur
Contains enzymes and specialised structures (organelles)
Cell surface membrane
Surrounds the cytoplasm
Partially permeable
Hence controls substances entering or leaving the cell
nucleoplasm nucleolus chromatin
nuclear envelope
Nucleus
Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin
Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

21. Nucleus

22. Nucleus- what is inside? Chromatin
-A network of thread-like structures in the nucleus
-It controls the activities of the cell, such as cell division
-Each chromatin is made up of proteins and deoxyribonucleic acid (DNA)
DNA contains:
-Hereditary information
-Instructions that a cell needs for carrying out all chemical reactions within itself.

23. Nucleus- what is inside? Chromosome
- When the cell is dividing, chromatin condenses and becomes highly coiled structures called chromosomes (which appear as thick, rod-shaped structures under light microscope)
chromosome

24. The Nucleus
Nucleus

25. The nucleus
Nucleus
Cheek cell
Onion epithelial cell

26. Vacuole -Fluid-filled space enclosed by a membrane Function:
-Contained in the cytoplasm
Function:
-Storage of substances within the cell

27. Water; food substances
Vacuole
Animal
Plant
Size and number
Small and many
Large and only one
Contents
Water; food substances
Cell sap (contains dissolved substances such as sugars, mineral salts and amino acids, enclosed by a membrane called tonoplast)
How long do they exist?
Temporarily
More permanent

28. Vacuole
Vacuole

29. Vacuole

30. Chloroplast -Oval structures found in plant cells
-Found in the cytoplasm
Function:
-Contains the green pigment chlorophyll, which is essential for plants to make food (the process of photosynthesis)

31. The chloroplast Chloroplast Only exist in plant cells
Absent in animal cells

32. Chloroplast
Photomicrograph
Chloroplasts

33. Chloroplast
Electronmicrograph

34. Mitochondria (sin: Mitochondrion)
-Small, sausage-shaped
-Can be seen clearly under electron microscope
Function:
- Aerobic respiration occurs in the mitochondria
-Aerobic respiration is the process whereby food substances are oxidised to give energy the cell needs to carry out activities like growth and reproduction

35. Mitochondria
Electronmicrograph
of mitochondrion

36. Mitochondria
Electron-
micrograph:

37. Mitochondria
Electron-
micrograph:
(b) A plant cell

38. Mitochondria
Electronmicrograph:

39. Ribosome
Small, round structures
Either attached to certain membranes in the cells or lie freely in the cytoplasm.
Function:
Synthesize proteins in the cell

40. Ribosomes
Electron-
micrograph:

41. In summary- Most cells share certain features:
Protoplasm
Cytoplasm
Nucleus
Gel-like substance
forming major part of cell
Site where most
organelles are found:
Mitochondria (sausage
shaped)
-for cell respiration
Centrioles -
involved in cell division
Chloroplasts -
Contains chlorophyll,
green pigment needed for
photosynthesis
Vacuoles -
fluid-filled storage sacs
Ribosomes-
Synthesise proteins
Cell surface membrane
Nucleoli- Building proteins
Nucleoplasm- small round
mass of protoplasm called
the nucleoplasm
Nuclear envelope-
Separates nuclear content
from the surrounding
Cytoplasm
Chromatin threads- Found in
nucleoplasm, contain
hereditary materials which
condense to form chromosomes
Partially permeable
membrane covering
of cell
Controls substances
entering and leaving cell

42. Cell seen under electron microscope

44. Rough endoplasmic reticulum
Rough endoplasmic reticulum (RER) has a surface that appears rough because of small particles called ribosomes that are attached to its outer surface. The outer surface of the RER is continuous with the nuclear envelope.
Ribosomes are small round structures that are either attached to the membrane of the RER or lie freely in the cytoplasm. They are needed to synthesise proteins.
The ribosomes attached to the RER make proteins that are usually transported out of the cell
The ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell.
The RER transports proteins made to the Golgi apparatus for secretion out of the cell.

45. Smooth endoplasmic reticulum
The smooth ER (SER) does not have ribosomes attached to its membrane. SER is more tubular that than the RER. It is connected to the RER.
The SER synthesises fats and steroids and converts harmful substances into harmless materials.

46. Golgi apparatus Golgi apparatus or Golgi body is shaped like a disc.
It consists of a stack of flattened spaces surrounded by membranes. Vesicles or tiny spherical spaces enclosed by a membrane can be seen fusing with one side of the Golgi apparatus and pinching off from the opposite side.
The Golgi apparatus stores and modifies substances made by the ER and packages these substances in vesicles for secretion out of the cell.

47. Plant and animal cells: Similarities
Both have nuclei
Both have cell membranes
Both have cytoplasm
Both have mitochondria, ribosomes, ER, Golgi apparatus, vesicles

48. Plant and animal cells: Differences
Plant cell
Many small vacuoles
A large central vacuole
Chloroplasts present
No chloroplasts
No cell wall
Cellulose cell wall
centrioles present
No centrioles
No regular shape
Regular shape

49. Differentiation Growth in an organism involves cell division.
New cells produced may change and develop into new tissues.
This process by which a cell becomes specialised for a specific function is called differentiation. Cells may develop special structures or lose certain structures for them to carry out specific functions.
e.g. Human cells become differentiated to form various types of cells:
liver cells, muscle cells, sperm cells, epithelial cells, blood cells, etc
e.g. Plant cells differentiate to form xylem cells, phloem cells, etc

50. Root Hair Cell Functions Adaptations
Long and narrow to increase the
surface area: volume ratio,
thus water and mineral salts can be efficiently absorbed from the soil.
Absorption of water & mineral salts from soil

51. Surface Area to Volume Ratio
Cube
Surface area/cm2
Volume/cm3
Surface area: volume
Side 1 cm
Side 2 cm
Side 3 cm
6:1
6 cm2
1 cm3
8 cm3
24 cm2
3:1
27 cm3
54 cm2
2:1

52. Xylem Vessels Functions Adaptations Long & thin tubes,
To conduct water & salts from roots to leaves
Long & thin tubes,
no cross walls or protoplasm which enables water to move easily through the lumen (central space)
To provide support for
stem & leaves
Lignin deposited on wall

53. Red Blood Cells Functions Adaptations -Circular biconcave, increases
the SA to Vol. ratio.
-no nucleus, enabling it to
contain more haemoglobin
To carry oxygen around the body

54. Tissues A group of cells work together to form a tissue. muscle cell
muscle tissue made up of muscle cells
epithelial cell
epithelial cell
gland cell
neurones
epithelium in the trachea (tissue) made up of epithelial cells and gland cells
epithelium in the lungs (tissue) made up of epithelial cells
nervous tissue made up of neurones (nerve cells)
connective tissue cell
intestinal epithelial cell
connective tissue cell
cartilage in the trachea (tissue) made up of connective tissue cells
connective tissue in the lungs made up of connective tissue cells
intestinal epithelium (tissue) made up of intestinal epithelial cells
A group of cells work together to form a tissue.

55. Tissue
A group of similar cells which work together to perform a specific function
-Cells of the same type form simple tissue
E.g. epidermis tissue (plants) and epithelial tissues (animals)
-Cells of different types form complex tissue
E.g. connective tissue (animals), blood, vascular tissue (plants)

56. intestinal epithelium (tissue)
Organs
muscle tissue
epithelium (tissue)
stomach (organ)
trachea (organ)
nervous tissue
cartilage (tissue)
intestinal epithelium (tissue)
epithelium (tissue)
lungs (organs)
intestine (organ)
muscle tissue
connective tissue
Different tissues combine to form an organ.

57. Systems Several organs work together to make up an organ system.
stomach (organ)
trachea (organ)
respiratory system (organ system)
digestive system (organ system)
lungs (organs)
intestine (organ)
Several organs work together to make up an organ system.

58. Specialised Cells, Tissues, Organs & Systems
digestive system (organ system)
respiratory system (organ system)
human (organism)
Various organ systems work together to make up an organism.

59. CELL Protoplasm Cellulose cell wall (found only in plants) Tissues
Organs
Organ systems
made up of
Organism
Protoplasm
Cellulose cell wall
(found only in plants)
consists of
Nucleus
Cytoplasm
Cell surface membrane
which
which
which
controls cell activities
surrounds the nucleus and is where most cell activities occur
is the partially permeable, outer covering enclosing the cytoplasm
and contains
contains organelles
Chromatin (made up of DNA)
Ribosomes (involved in protein synthesis)
Mitochondria (sites of energy release)
Chloroplasts (in plant cells)
Vacuoles (contain water and food substances)

60. You should be able to:
Know the functions and identify from diagram and photomicrographs, the nucleus, chloroplast, ribosome, mitochondrion, endoplasmic reticulum.
Examine under the microscope an animal cell
(from fresh liver& human check cell) and
a plant cell (from Hydrilla & onion )
Compare and contrast the structures of plant and animal cell
Relate the adaptations of a cell structure to its functions for the following: Absorption-root hair cells/ Conduction and support- xylem vessels /Transport of oxygen-red blood cells
Differentiate between the terms cell, tissues, organ and organ system.